D1 has no interactive transactions. Here is what to do instead.

Cloudflare D1 does not support interactive transactions. db.transaction() throws at runtime, and no amount of Drizzle configuration changes that: the constraint is in the platform, because a transaction that stays open across round trips is exactly what a distributed SQLite cannot offer.

That matters the moment you have a balance to spend.

The naive version, and why it loses money

const { balance } = await db.select(...)   // read
if (balance < cost) throw new Error('insufficient')
await db.update(...).set({ balance: balance - cost })   // write

Two requests arriving together both read the same balance, both pass the check, and both write. The account goes negative, and the ledger no longer explains how.

The fix: make the check part of the write

Do not read, decide, then write. Write conditionally, and let the database decide:

const spent = await db
  .update(credits)
  .set({ balance: sql`${credits.balance} - ${cost}` })
  .where(and(eq(credits.userId, userId), gte(credits.balance, cost)))
  .returning({ balance: credits.balance })

if (!spent.length) throw new InsufficientCredits()

One statement. The gte in the WHERE is the balance check, so it is evaluated under the same lock as the update. Zero rows back means it did not apply — the caller learns that from the row count, not from a prior read.

When one statement is not enough

Spending usually also writes a ledger row, and you want both or neither. That is what db.batch() is for: several statements, one round trip, applied atomically. It is not an interactive transaction — you cannot branch on the result of the first statement — but for "these writes go together" it is exactly right.

await db.batch([
  db.update(credits).set(...).where(...),
  db.insert(ledger).values(...),
])

The rule of thumb

If a decision depends on current state, push the decision into the WHERE clause. If several writes must land together, use batch(). If you find yourself wanting to read, branch in JavaScript, and then write — that is the shape D1 cannot give you, and it is worth restructuring before it becomes a bug you only see under load.